Fungal Genetics and Biology

Manual annotation of the Phytophthora ramorum and P. sojae genomes has identified 136, and 132 members, respectively, indicating that the ABC superfamily is comparable in size to the Arabidopsis and rice genomes. The high level of synteny that was observed between these oomycete genomes extends to the ABC superfamily where 107 orthologous pairs were identified by phylogenetic analysis. The largest subfamilies in the oomycetes include those most often associated with multidrug resistance. The P. ramorum genome contains 22 multidrug resistance-associated protein (MRP) genes, and 48 pleiotropic drug resistance (PDR) genes, while P. sojae contains 20 MRP, and 46 PDR genes. Tandem duplication events in the last common ancestor appear to account for much of the expansion of these subfamilies. Phylogenetic comparisons of membrane transporters from the multidrug resistance (MDR), MRP and PDR subfamilies with Arabidopsis and human genes, show that the majority of oomycete transporters clustering in separate resolved nodes. Moreover, genetic variability within these oomycete subfamilies is greater than that seen in other eukaryotic kingdoms. The oomycete genomes also contains three examples of bacterial type ABC transporters. These include one example of an ABCB half transporter, and components of two ABC transporters associated with iron and molybdenum acquisition. Thus, the oomycetes appear to have taken maximum advantage of the architecture of these proteins to catalyze the transport of compounds across membranes.